Abstract

ABSTRACT. Detrital deposition processes: a new method of determination applied on cave fillings. Pierre-la-Treiche caves (Lorraine, France) are largely filled with alluvial deposits, carried by the Moselle river in the past. Some sedimentological studies have been carried out, with the aim of defining the hydrodynamic features of the deposition of these cave fillings. Thus, some grain analyses have allowed to identify different parameters of palaeoflows and of transport and deposition of detrital sediments, both by applying former interpretative patterns and by studying new representations. Results are often given as frequencies cumulative curves, that deliver a complete grain-size picture. However, a high number of analyses makes comparisons difficult between samples and the use of synthetic coefficients should be preferred. Quantiles and derived indices, such as mean size, standard deviation, asymmetry, are classical approaches to determine competence, average power, flow regularity, fluvial dynamics, etc. Some correlations of indices may turn out to be interesting too. Thus, the classic Passega's diagram (or CM picture) reveals the mode of transport of particles, that is the hydrological dynamics. In the same way, it is possible to obtain a good grain-size representation of a sample, by correlating its mean size and its standard deviation coefficient, that respectively convey the position in abscissa and the slope of the cumulative curve. The resulting " distribution " graph allows to define the deposition process, and usefully completes the CM picture interpretations.